crypto/ec/ec_backend.c

   1 /*
   2  * Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #include <openssl/core_names.h>
  11 #include <openssl/objects.h>
  12 #include <openssl/params.h>
  13 #include <openssl/err.h>
  14 #include "crypto/bn.h"
  15 #include "crypto/ec.h"
  16 #include "ec_local.h"
  17 #include "e_os.h"
  18 #include "internal/param_build_set.h"
  19
  20 /* Mapping between a flag and a name */
  21 static const OSSL_ITEM encoding_nameid_map[] = {
  22     { OPENSSL_EC_EXPLICIT_CURVE, OSSL_PKEY_EC_ENCODING_EXPLICIT },
  23     { OPENSSL_EC_NAMED_CURVE, OSSL_PKEY_EC_ENCODING_GROUP },
  24 };
  25
  26 int ec_encoding_name2id(const char *name)
  27 {
  28     size_t i, sz;
  29
  30     /* Return the default value if there is no name */
  31     if (name == NULL)
  32         return OPENSSL_EC_NAMED_CURVE;
  33
  34     for (i = 0, sz = OSSL_NELEM(encoding_nameid_map); i < sz; i++) {
  35         if (strcasecmp(name, encoding_nameid_map[i].ptr) == 0)
  36             return encoding_nameid_map[i].id;
  37     }
  38     return -1;
  39 }
  40
  41 static char *ec_param_encoding_id2name(int id)
  42 {
  43     size_t i, sz;
  44
  45     for (i = 0, sz = OSSL_NELEM(encoding_nameid_map); i < sz; i++) {
  46         if (id == (int)encoding_nameid_map[i].id)
  47             return encoding_nameid_map[i].ptr;
  48     }
  49     return NULL;
  50 }
  51
  52 int ec_group_todata(const EC_GROUP *group, OSSL_PARAM_BLD *tmpl,
  53                     OSSL_PARAM params[], OSSL_LIB_CTX *libctx,
  54                     const char *propq,
  55                     BN_CTX *bnctx, unsigned char **genbuf)
  56 {
  57     int ret = 0, curve_nid, encoding_flag;
  58     const char *field_type, *encoding_name;
  59     const BIGNUM *cofactor, *order;
  60     BIGNUM *p = NULL, *a = NULL, *b = NULL;
  61     point_conversion_form_t genform;
  62     const EC_POINT *genpt;
  63     unsigned char *seed = NULL;
  64     size_t genbuf_len, seed_len;
  65
  66     if (group == NULL) {
  67         ECerr(0,EC_R_PASSED_NULL_PARAMETER);
  68         return 0;
  69     }
  70
  71     encoding_flag = EC_GROUP_get_asn1_flag(group) & OPENSSL_EC_NAMED_CURVE;
  72     encoding_name = ec_param_encoding_id2name(encoding_flag);
  73     if (encoding_name == NULL
  74         || !ossl_param_build_set_utf8_string(tmpl, params,
  75                                              OSSL_PKEY_PARAM_EC_ENCODING,
  76                                              encoding_name)) {
  77         ECerr(0, EC_R_INVALID_ENCODING);
  78         return 0;
  79     }
  80
  81     curve_nid = EC_GROUP_get_curve_name(group);
  82     if (curve_nid == NID_undef) {
  83         /* explicit curve */
  84         int fid = EC_GROUP_get_field_type(group);
  85
  86         if (fid == NID_X9_62_prime_field) {
  87             field_type = SN_X9_62_prime_field;
  88         } else if (fid == NID_X9_62_characteristic_two_field) {
  89             field_type = SN_X9_62_characteristic_two_field;
  90         } else {
  91             ECerr(0, EC_R_INVALID_FIELD);
  92             return 0;
  93         }
  94
  95         p = BN_CTX_get(bnctx);
  96         a = BN_CTX_get(bnctx);
  97         b = BN_CTX_get(bnctx);
  98         if (b == NULL) {
  99             ECerr(0, ERR_R_MALLOC_FAILURE);
 100             goto err;
 101         }
 102
 103         if (!EC_GROUP_get_curve(group, p, a, b, bnctx)) {
 104             ECerr(0, EC_R_INVALID_CURVE);
 105             goto err;
 106         }
 107
 108         order = EC_GROUP_get0_order(group);
 109         if (order == NULL) {
 110             ECerr(0, EC_R_INVALID_GROUP_ORDER);
 111             goto err;
 112         }
 113         genpt = EC_GROUP_get0_generator(group);
 114         if (genpt == NULL) {
 115             ECerr(0, EC_R_INVALID_GENERATOR);
 116             goto err;
 117         }
 118         genform = EC_GROUP_get_point_conversion_form(group);
 119         genbuf_len = EC_POINT_point2buf(group, genpt, genform, genbuf, bnctx);
 120         if (genbuf_len == 0) {
 121             ECerr(0, EC_R_INVALID_GENERATOR);
 122             goto err;
 123         }
 124
 125         if (!ossl_param_build_set_utf8_string(tmpl, params,
 126                                               OSSL_PKEY_PARAM_EC_FIELD_TYPE,
 127                                               field_type)
 128             || !ossl_param_build_set_bn(tmpl, params, OSSL_PKEY_PARAM_EC_P, p)
 129             || !ossl_param_build_set_bn(tmpl, params, OSSL_PKEY_PARAM_EC_A, a)
 130             || !ossl_param_build_set_bn(tmpl, params, OSSL_PKEY_PARAM_EC_B, b)
 131             || !ossl_param_build_set_bn(tmpl, params, OSSL_PKEY_PARAM_EC_ORDER,
 132                                         order)
 133             || !ossl_param_build_set_octet_string(tmpl, params,
 134                                                   OSSL_PKEY_PARAM_EC_GENERATOR,
 135                                                   *genbuf, genbuf_len)) {
 136             ECerr(0, ERR_R_MALLOC_FAILURE);
 137             goto err;
 138         }
 139
 140         cofactor = EC_GROUP_get0_cofactor(group);
 141         if (cofactor != NULL
 142             && !ossl_param_build_set_bn(tmpl, params,
 143                                         OSSL_PKEY_PARAM_EC_COFACTOR, cofactor)) {
 144             ECerr(0, ERR_R_MALLOC_FAILURE);
 145             goto err;
 146         }
 147
 148         seed = EC_GROUP_get0_seed(group);
 149         seed_len = EC_GROUP_get_seed_len(group);
 150         if (seed != NULL
 151             && seed_len > 0
 152             && !ossl_param_build_set_octet_string(tmpl, params,
 153                                                   OSSL_PKEY_PARAM_EC_SEED,
 154                                                   seed, seed_len)) {
 155             ECerr(0, ERR_R_MALLOC_FAILURE);
 156             goto err;
 157         }
 158 #ifdef OPENSSL_NO_EC2M
 159         if (fid == NID_X9_62_characteristic_two_field) {
 160             ECerr(0, EC_R_GF2M_NOT_SUPPORTED);
 161             goto err;
 162         }
 163 #endif
 164     } else {
 165         /* named curve */
 166         const char *curve_name = ec_curve_nid2name(curve_nid);
 167
 168         if (curve_name == NULL
 169             || !ossl_param_build_set_utf8_string(tmpl, params,
 170                                                  OSSL_PKEY_PARAM_GROUP_NAME,
 171                                                  curve_name)) {
 172             ECerr(0, EC_R_INVALID_CURVE);
 173             goto err;
 174         }
 175     }
 176     ret = 1;
 177 err:
 178     return ret;
 179 }
 180
 181 /*
 182  * The intention with the "backend" source file is to offer backend support
 183  * for legacy backends (EVP_PKEY_ASN1_METHOD and EVP_PKEY_METHOD) and provider
 184  * implementations alike.
 185  */
 186 int ec_set_ecdh_cofactor_mode(EC_KEY *ec, int mode)
 187 {
 188     const EC_GROUP *ecg = EC_KEY_get0_group(ec);
 189     const BIGNUM *cofactor;
 190     /*
 191      * mode can be only 0 for disable, or 1 for enable here.
 192      *
 193      * This is in contrast with the same parameter on an ECDH EVP_PKEY_CTX that
 194      * also supports mode == -1 with the meaning of "reset to the default for
 195      * the associated key".
 196      */
 197     if (mode < 0 || mode > 1)
 198         return 0;
 199
 200     if ((cofactor = EC_GROUP_get0_cofactor(ecg)) == NULL )
 201         return 0;
 202
 203     /* ECDH cofactor mode has no effect if cofactor is 1 */
 204     if (BN_is_one(cofactor))
 205         return 1;
 206
 207     if (mode == 1)
 208         EC_KEY_set_flags(ec, EC_FLAG_COFACTOR_ECDH);
 209     else if (mode == 0)
 210         EC_KEY_clear_flags(ec, EC_FLAG_COFACTOR_ECDH);
 211
 212     return 1;
 213 }
 214
 215 /*
 216  * Callers of ec_key_fromdata MUST make sure that ec_key_params_fromdata has
 217  * been called before!
 218  *
 219  * This function only gets the bare keypair, domain parameters and other
 220  * parameters are treated separately, and domain parameters are required to
 221  * define a keypair.
 222  */
 223 int ec_key_fromdata(EC_KEY *ec, const OSSL_PARAM params[], int include_private)
 224 {
 225     const OSSL_PARAM *param_priv_key = NULL, *param_pub_key = NULL;
 226     BN_CTX *ctx = NULL;
 227     BIGNUM *priv_key = NULL;
 228     unsigned char *pub_key = NULL;
 229     size_t pub_key_len;
 230     const EC_GROUP *ecg = NULL;
 231     EC_POINT *pub_point = NULL;
 232     int ok = 0;
 233
 234     ecg = EC_KEY_get0_group(ec);
 235     if (ecg == NULL)
 236         return 0;
 237
 238     param_pub_key =
 239         OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_PUB_KEY);
 240     if (include_private)
 241         param_priv_key =
 242             OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_PRIV_KEY);
 243
 244     ctx = BN_CTX_new_ex(ec_key_get_libctx(ec));
 245     if (ctx == NULL)
 246         goto err;
 247
 248     /* OpenSSL decree: If there's a private key, there must be a public key */
 249     if (param_priv_key != NULL && param_pub_key == NULL)
 250         goto err;
 251
 252     if (param_pub_key != NULL)
 253         if (!OSSL_PARAM_get_octet_string(param_pub_key,
 254                                          (void **)&pub_key, 0, &pub_key_len)
 255             || (pub_point = EC_POINT_new(ecg)) == NULL
 256             || !EC_POINT_oct2point(ecg, pub_point, pub_key, pub_key_len, ctx))
 257         goto err;
 258
 259     if (param_priv_key != NULL && include_private) {
 260         int fixed_words;
 261         const BIGNUM *order;
 262
 263         /*
 264          * Key import/export should never leak the bit length of the secret
 265          * scalar in the key.
 266          *
 267          * For this reason, on export we use padded BIGNUMs with fixed length.
 268          *
 269          * When importing we also should make sure that, even if short lived,
 270          * the newly created BIGNUM is marked with the BN_FLG_CONSTTIME flag as
 271          * soon as possible, so that any processing of this BIGNUM might opt for
 272          * constant time implementations in the backend.
 273          *
 274          * Setting the BN_FLG_CONSTTIME flag alone is never enough, we also have
 275          * to preallocate the BIGNUM internal buffer to a fixed public size big
 276          * enough that operations performed during the processing never trigger
 277          * a realloc which would leak the size of the scalar through memory
 278          * accesses.
 279          *
 280          * Fixed Length
 281          * ------------
 282          *
 283          * The order of the large prime subgroup of the curve is our choice for
 284          * a fixed public size, as that is generally the upper bound for
 285          * generating a private key in EC cryptosystems and should fit all valid
 286          * secret scalars.
 287          *
 288          * For padding on export we just use the bit length of the order
 289          * converted to bytes (rounding up).
 290          *
 291          * For preallocating the BIGNUM storage we look at the number of "words"
 292          * required for the internal representation of the order, and we
 293          * preallocate 2 extra "words" in case any of the subsequent processing
 294          * might temporarily overflow the order length.
 295          */
 296         order = EC_GROUP_get0_order(ecg);
 297         if (order == NULL || BN_is_zero(order))
 298             goto err;
 299
 300         fixed_words = bn_get_top(order) + 2;
 301
 302         if ((priv_key = BN_secure_new()) == NULL)
 303             goto err;
 304         if (bn_wexpand(priv_key, fixed_words) == NULL)
 305             goto err;
 306         BN_set_flags(priv_key, BN_FLG_CONSTTIME);
 307
 308         if (!OSSL_PARAM_get_BN(param_priv_key, &priv_key))
 309             goto err;
 310     }
 311
 312     if (priv_key != NULL
 313         && !EC_KEY_set_private_key(ec, priv_key))
 314         goto err;
 315
 316     if (pub_point != NULL
 317         && !EC_KEY_set_public_key(ec, pub_point))
 318         goto err;
 319
 320     ok = 1;
 321
 322  err:
 323     BN_CTX_free(ctx);
 324     BN_clear_free(priv_key);
 325     OPENSSL_free(pub_key);
 326     EC_POINT_free(pub_point);
 327     return ok;
 328 }
 329
 330 int ec_group_fromdata(EC_KEY *ec, const OSSL_PARAM params[])
 331 {
 332     int ok = 0;
 333     EC_GROUP *group = NULL;
 334
 335     if (ec == NULL)
 336         return 0;
 337
 338      group = EC_GROUP_new_from_params(params, ec_key_get_libctx(ec),
 339                                       ec_key_get0_propq(ec));
 340
 341     if (!EC_KEY_set_group(ec, group))
 342         goto err;
 343
 344     /*
 345      * TODO(3.0): if the group has changed, should we invalidate the private and
 346      * public key?
 347      */
 348     ok = 1;
 349 err:
 350     EC_GROUP_free(group);
 351     return ok;
 352 }
 353
 354 int ec_key_otherparams_fromdata(EC_KEY *ec, const OSSL_PARAM params[])
 355 {
 356     const OSSL_PARAM *p;
 357
 358     if (ec == NULL)
 359         return 0;
 360
 361     p = OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_USE_COFACTOR_ECDH);
 362     if (p != NULL) {
 363         int mode;
 364
 365         if (!OSSL_PARAM_get_int(p, &mode)
 366             || !ec_set_ecdh_cofactor_mode(ec, mode))
 367             return 0;
 368     }
 369
 370     return 1;
 371 }